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 138 Vol. XX THE YOLLA BOLLY FOX SPARROW By JOSEPH MAILLIARD S WE BECOME better acquainted with the genus Passerella we find it proving to be one of the most plastic forms of our North American avi- fauna. It bids fair to rival even the Melospiza group, which has been split up into subspecies from so many different localities that it is hard to keep track of them. It has been said that we have song sparrows described from every marsh in California! While this is not literally true, there certainly are re- markable differences in a great many instances, and we are finding the same sort of thing in the fox sparrows. For some years students interested along these lines, especially observers on the Pacific coast, have been sorely puzzled by the differences among individual specimens of Passerella found in winter in the same localitias. These differ- ences were such as could only be accounted for upon the hypothesis that they indicated separate forms, each with its definite breeding ground, and not that they were individual variations of any one race. As time goes on and we have more numerous and widespread records, with more detailed observations, we are discovering that this hypothesis is the correct one. Readers of TH CONDO1 may remember that their attention was called to the occurrence in winter in Marin County, California, of a very large-billed fox sparrow which seemed more nearly related to the Stephens Fox Sparrow (Pass- erella iliaca stephensi) than to any other known form (CoNDOle, xv, March, 1912, p. 63). Alternative explanations of this occurrence were that either there was an undiscovered race closely approaching stephensi breeding somewhere to the north of Marin County, which it visited in winter; or else, contrary to the rule that in the northern hemisphere birds do not winter north of their breed- ing range, these individuals were actually examples of stephensi which had straggled northward in the winter season. At the time I first took up this mat- ter the only specimens of stephensi available for comparison were in worn sum- mer plumage, while the Marin County birds'were in bright new feather. This made the comparison very unsatisfactory, in that the difference in color might be accounted for by this fact. Measurements of parts unaffected by wear were practically identical in the two lots. This Marin County form was again men- tioned in TH CoN, Old, xv, March, 1913, p. 93. Since that time material has been accumulated in the way of breeding birds obtained in Trinity and Tehama counties, California, by col- lectors from the Museum of Vertebrate Zoology of the University of Califor- nia, which proves that there actually is a race of fox sparrow breeding to the north, as already suspected. But this form, for want of sufficient material for seasonal comparison, was still linked up with stephensi of southern and south- eastern California. Recently, however, Mr. H. S. Swarth of the Museum of Vertebrate Zoology, has become interested in the status of the Passerella group and has gotten together a large number of specimens for comparative study. While working over these he came across just the sort of material needed to put together the chain of eviden. ce in favor of the distinctness of this new form, and kindly notified me of the fact, we having often discussed this matter to- gether. As he is working out the status of the subspecies of Passerella on this